General Motors Corp. reportedly will assemble its new twin-cam, all aluminum L850 engine family at three facilities around the globe. The powerplant, expected to appear in every small GM car in Europe and North America, will roll off three production lines: Tonawanda, NY; Aspern, Austria; and Port Melbourne, Australia. Production is expected to fire up in late 1997, press reports indicate. Both gas and diesel engines will be offered with a maximum displacement of 2.2L. Annual volume will reach 1.5 million units by 2002 or 2003. Total investment for the engine family tops $1 billion.